Answers to Questions
How to encrypt using AMSCO cipher?
AMSCO Encryption consists in writing a text in a grid according to a cutting sequence then use a permutation key to switch columns.
Example: Encrypt the message DCODEAMSCO, with a cutting sequence 1,2 (alternation of 1 letter then 2 letters in the grid)
Select a permutation key (of length L), and write the message in lines, cut over L columns.
Example: If the key is KEY (equivalent to 2,1,3) of length 3, then write the message over 3 columns :
Read the grid in columns, in the order of the key (this reading serves as permutation).
Example: Column 2 (COM) then 1 (DEAO), and the 3 (DSC). The message is COMDEAODSC.
How to decrypt AMSCO cipher?
AMSCO decryption requires knowledge of the permutation key (of length L) and the cutting sequence (usually 1,2 or 2,1).
Example: Decrypt the message COMDEAODSC (of 10-characters length) with the key KEY (equivalent to the permutation 2,1,3) of length 3, and cutting sequence 1.2.
Create a table with L columns, in which the number of characters are noted in each cell (in respect to the cutting sequence and limited by the length of the message).
Example: 1,2 for 10 characters corresponds to (1+2+1+2+1+2+1+0+0 = 10) :
Write the message in the table in columns following the order of the columns indicated by the key.
Example: Write CO, then M in column 2, then D,EA,O in column 1, then D, DC in column 3. This leads to the grid:
The plain message is transcribed by reading the table in lines.
Example: Reading each lines gives the original plain text is DCODEAMSCO.
How to correctly split the text into the grid?
The text must alternate sizes of cuts which then should form diagonal sets:
Example: A grid of width 3, cut by (1,2):
Example: A grid of width 3, cut by (2,1):
Example: A grid of width 4, cut by (1,2):
Example: A grid of width 3, cut by (3,2,1):
How to recognize AMSCO ciphertext?
How to decipher AMSCO without key?
It is possible to try to infer the key length by analyzing bigrams obtained after writing in columns.
What are the variants of the AMSCO cipher?
AMSCO is a variant of the classical transposition cipher. It adds the cut sequence that can be more complex than the usual 1,2.
When AMSCO have been invented?
By A. M. Scott, in the 19th century